Re: Another OBC problem

[Brianmoooore]

I posted on the old forum last week about a problem with my newly fitted OBC, with the gong emitting a continuous tone at a low, but audible level. I had plenty of views of my post but no relevant replies, so just in case anyone else gets this problem, here is my solution.
First I established that the wires to the gong are ground, 12V+, and 'ground to sound gong ', and that the fault was in the gong itself.
I opened up the gong and traced out it's circuit. It consists of a single transistor audio amplifier and speaker, a pair of NAND gates forming a continuously running astable oscilator, a simple diode gate to isolate the oscilator from the amp and another NAND gate and transistor forming a pulse generator and envelope shaper, which transforms the continuous oscilator into the gong sound.
My problem was that the gate wasn't quite closing, so letting through the tone from the oscilator. I changed or checked every part relevant to the gate, but still couldn't solve the problem, so eventually I added a couple of 8.2k ohm resistors, one to 12V+, and one to ground either side of the diode gate to reverse bias it a bit more. This solved the problem.

[kidsinister]

I simply must protest at the level of techiness in this post. Hitting it with a hammer not good enough for you eh?

Alec

[Simon]

Must say all that went straight over my head too!